Motors using rare-earth permanent magnets with high magnetic performance are actively used for various devices. On the other hand, in view of the exhaustion of the earth's resources, motors designed to reduce the usage of rare-earth permanent magnets to a minimum are being studied.
Japanese Patent Application Publication No. 2004-357489 discloses a motor with a consequent pole rotor as an example of the latter type of motors; this motor will be also referred to as a “consequent pole motor”.
The consequent pole motor disclosed in the patent Publication is comprised of a plurality of permanent magnet poles with the same magnetic polarity, such as the north or south pole, in the outer periphery of a cylindrical soft magnetic rotor. The cylindrical soft magnetic rotor is designed as a consequent pole rotor to have a plurality of radially outwardly projections disposed respectively between the plurality of permanent magnet poles so that the magnetic polarities of the plurality of permanent magnet poles cause the plurality of projections to be consequently magnetized as the same magnetic polarity opposite to the magnetic polarity of the plurality of permanent magnet poles. Such a consequent pole motor includes a number of permanent magnet poles, which is half that of the permanent magnet poles of normal permanent magnet motors, thus maintaining its magnetic performance with reduction in the number of the permanent magnet poles.
On the other hand, concentrated winding motors are mainly used for various devices. 12-slot, 10-pole motors with concentrated winding or 12-slot, 14-pole motors with concentrated winding, which have a relatively high winding factor, have been proposed in order to limit the deterioration in magnetic performance of these motors.
For example, FIG. 9 is a table schematically illustrating a correlation between electrical angles of teeth of the armature of a 12-slot, 10-pole motor and mechanical angles of the corresponding teeth per rotation of 360 mechanical angle (equal to 1800 electrical angle) of the 10-pole rotor assuming that one of the teeth is a reference tooth at the electrical angle and mechanical angle of 0, FIG. 10 is a table schematically illustrating a correlation between: index numbers 1, 2, . . . , 12 assigned to the teeth from the tooth adjacent to the reference tooth in a counterclockwise direction to the reference tooth of the 12-slot, 10-pole motor, electrical angles of the corresponding teeth 1, 2, . . . , 12 of the armature of the 12-slot, 10-pole motor, and mechanical angles of the corresponding teeth 1, 2, . . . , 12. As illustrated in FIGS. 9 and 10, one cycle of the rotating magnetic field created by armature currents corresponds to 360 electrical degrees, and therefore, 0 electrical degrees is in agreement with 360 electrical degrees.